Magnetic and MO media are widely employed in various applications, particularly in the computer industry for data/information storage and retrieval purposes. A magnetic medium in e.g., disc form, such as utilized in computer-related applications, comprises a non-magnetic disc-shaped substrate, e.g., of glass, ceramic, glass-ceramic composite, polymer, metal, or metal alloy, typically an aluminum (Al)-based alloy such as aluminum-magnesium (Al—Mg), having at least one major surface on which a layer stack or laminate comprising a plurality of thin film layers constituting the medium are sequentially deposited. Such layers may include, in sequence from the substrate deposition surface, a plating layer, e.g., of amorphous nickel-phosphorus (Ni—P), a polycrystalline underlayer, typically of chromium (Cr) or a Cr-based alloy such as chromium-vanadium (Cr—V), a magnetic layer, e.g., of a cobalt (Co)-based alloy, and a protective overcoat layer, typically of a carbon (C)-based material having good tribological properties. A similar situation exists with MO media, wherein a layer stack or laminate is formed on a substrate deposition surface, which layer stack or laminate comprises a reflective layer, typically of a metal or metal alloy, one or more rare-earth thermo-magnetic (RE-TM) alloy layers, one or more transparent dielectric layers, and a protective overcoat layer, for functioning as reflective, transparent, writing, writing assist, and read-out layers, etc.
Thin film magnetic and MO media in disc form, such as described supra, are typically lubricated with a thin film of a polymeric lubricant, e.g., a perfluoropolyether, to reduce wear of the disc when utilized with data/information recording and read-out heads/transducers operating at low flying heights, as in a hard disc system functioning in a contact start-stop (“CSS”) mode. Conventionally, a thin film of lubricant is applied to the disc surface(s) during manufacture by dipping into a bath containing a small amount of lubricant, e.g., less than about 1% by weight of a fluorine-containing polymer, dissolved in a suitable solvent, typically a perfluorocarbon, fluorohydrocarbon, or hydrofluoroether. However, a drawback inherent in such dipping process is the consumption of large quantities of solvent, resulting in increased manufacturing cost and concern with environmental hazards associated with the presence of toxic or otherwise potentially harmful solvent vapors in the workplace.
Another drawback associated with the conventional dipping method for applying a thin film of a polymeric lubricant to a substrate results from the lubricant materials being mixtures of long chain polymers, with a distribution of molecular weights. Since the molecular weight of the polymeric lubricant affects the mechanical (i.e., tribological) performance of the head-disc interface, it is common practice to subject the polymeric lubricant mixtures (as supplied by the manufacturer) to a fractionation process prior to adding the lubricant to the solvent in order to obtain a fraction having a desired molecular weight distribution providing optimal tribological performance. However, such pre-fractionation undesirably adds an additional step and increases the overall process cost.
Vapor deposition of thin film lubricants is an attractive alternative to dip lubrication in view of the above drawbacks. Specifically, vapor deposition of lubricant films is advantageous in that it is a solventless process and the process for generating the lubricant vapor can simultaneously serve for fractionating the lubricant mixture into a desired molecular weight distribution, thereby eliminating the need for a pre-fractionation step. Moreover, vapor deposition techniques can provide up to about 100% bonded lubricant molecules when utilized with appropriate polymeric lubricants and magnetic and/or MO disc substrates having deposition surfaces comprised of a freshly-deposited carbon-based protective overcoat layer which is not exposed to air prior to lubricant deposition thereon.
However, existing vapor deposition apparatus (e.g., the Intevac VLS 100 system, Intevac Corp., Santa Clara, Calif., described in detail in U.S. Pat. No. 6,183,831 B1, the disclosure of which is incorporated herein by reference) for applying a thin layer of polymeric lubricant to a thin film data/information storage and retrieval medium, e.g., in disc form, utilize a static process/system, wherein a single disc-shaped substrate is moved (e.g., by means of a disc lifter) to a position facing the orifices of a pair of oppositely facing lubricant vapor sources and statically maintained at that position while the lubricant film is deposited on the disc surfaces, with the lubricant film thickness being determined (i.e., controlled) by the length of the interval during which the disc surfaces are statically maintained facing the orifices of the lubricant vapor sources.
In order to control the spatial distribution, hence thickness uniformity, of the lubricant thin films obtained with such static vapor deposition process/apparatus at deposition rates of from about 1 to about 10 Å/sec. for providing lubricant film thicknesses up to about 50 Å, a diffuser plate for the lubricant vapor is provided intermediate the lubricant vapor source and the substrate surface, thereby adding to the system complexity and necessitating periodic maintenance of the diffuser plate for ensuring clear vapor passage through each of the openings in the diffuser plate. In addition, such static vapor lubrication systems incur a drawback when utilized as part of an in-line or similar type multi-chamber or modular system for manufacturing magnetic or MO media, in that a line-of-sight path is required for the mechanism utilized for positioning the disc surface opposite the lubricant vapor source. As a result, a path can be established for the lubricant vapor to escape from the lubricant deposition chamber into adjacent process chambers utilized for different processing functions and result in their being contaminated with lubricant vapor.
In addition to the above drawbacks, lubricant vapor deposition of disc substrates utilizing apparatus such as described in the aforementioned U.S. Pat. No. 6,183,831 B1 incurs several additional drawbacks and disadvantages, as follows:                while the process for generating the lubricant vapor can simultaneously serve for fractionating the lubricant mixture into a desired molecular weight distribution, thereby eliminating the need for a pre-fractionation step, when the finite amount of polymeric lubricant mixture initially contained in the vapor source is evaporated, the lighter, lower molecular weight (“MW”) molecules tend to evaporate first, leading to variation of the average MW of the deposited lubricant over time, which variation in turn results in a variation of the properties of the resultant lubricant films over time;        the single disc vapor deposition apparatus of U.S. Pat. No. 6,183,831 B1 typically forms part (i.e., a module) of a continuously operable, in-line apparatus for automated manufacture of magnetic or MO disc media, e.g., an Intevac MDP 250B Magnetic Disc Coater (as described in U.S. Pat. No. 5,215,420, the disclosure of which is incorporated herein by reference). However, combination of the single disc vapor deposition apparatus with the continuously operable, in-line apparatus for automated manufacture results in a significant reduction in product throughput, in that the latter apparatus is capable of processing approximately six times the number of discs that can be processed in a given period of time by the single disc vapor deposition apparatus of U.S. Pat. No. 6,183,831 B1;        the stream of lubricant vapor formed by the vapor sources in the apparatus of U.S. Pat. No. 6,183,831 B1 is circularly-shaped, and thus unable to provide a uniform thickness lubricant layer on a plurality of discs transported past the source on a conveyor means such as a pallet;        the lubricant vapor sources in the apparatus of U.S. Pat. No. 6,183,831 B1 lack provision for maintaining a constant distribution of lubricant MWs, inasmuch as the lubricant is evaporated from a reservoir within the respective sources which can only be manually replenished (i.e., filled), necessitating interrupting operation of the apparatus and opening of the chamber of the vapor lubricant module;        when, as indicated supra, the vapor deposition apparatus of U.S. Pat. No. 6,183,831 B1 forms part (i.e., a module) of a continuously operable, in-line apparatus for automated manufacture of magnetic or MO disc media (e.g., an Intevac MDP 250B Magnetic Disc Coater), operation of the vapor deposition module or portion of the system entails removing discs from a cassette which holds up to 25 freshly carbon-coated discs unexposed to air, and vapor lubricant coating the discs one-at-a-time. Because the first disc removed from the cassette for vapor lubrication is always colder than the last, due to its shorter residence time in the vapor lubrication main chamber prior to being subjected to lubricant vapor deposition thereon, the resultant lubricant coating on the first disc is thicker than that formed on the last disc. Further, since discs at the ends of the cassette radiate heat to different surfaces than interiorly-located discs, they also attain different temperatures prior to lubricant deposition thereon and therefore exhibit corresponding variations in lubricant coating thickness; and        the apparatus of U.S. Pat. No. 6,183,831 B1 does not provide for removal of lubricant from the cassettes prior to their re-insertion into the apparatus for re-use.        
In view of the above, there exists a clear need for improved means and methodology for depositing thin films of a lubricant, e.g., a polymeric lubricant, by vapor techniques and at deposition rates consistent with the throughput requirements of automated manufacturing processing, e.g., of magnetic and/or MO data/information storage and retrieval media, which means and methodology overcome the above-described drawbacks and disadvantages of the conventional static lubricant vapor deposition technology. More specifically, there exists a need for improved means and methodology for vapor depositing thin films of lubricant (e.g., a polymeric lubricant) which provides improved lubricant film thickness uniformity over the entire deposition area of disc-shaped substrates utilized in the manufacture of such magnetic and/or MO media.
The present invention addresses and solves problems and difficulties in achieving uniform thickness lubricant thin film deposition over a plurality of disc-shaped substrates by means of vapor deposition techniques, e.g., thin film polymeric lubricant deposition on disc substrates utilized in the manufacture of magnetic and/or MO media, while maintaining full capability with all aspects of conventional automated manufacturing technology therefor. Further, the means and methodology afforded by the present invention enjoy diverse utility in the manufacture of various other devices and articles requiring deposition of uniform thickness thin film lubricant layers thereon.